A Brief History of Harley-Davidson V-Twins

Harley Davidson V-twin engines have been around almost as long as their motorcycles. V-twins get their name from the distinctive V-shape formed by the angle between their two opposing cylinders. Harley Davidson introduced their first V-twin in 1909, and America (and eventually the world) began the enduring love affair with this icon of American motorcycles.

Six years after the introduction of their first production motorcycle, Harley Davidson produced their first V-twin engine in 1909. The two cyclinders were configured in a 45 degree vee, and were the precursor of things to come. The engine produced 7 horsepower from it's 49.5 cubic inch (CI) displacement.

Introduced in 1911, the F-Head enjoyed an 18 year run. On the back of the F-Head, Harley Davidson began exporting motorcycles to Japan, and formed their first Racing Department. Within two years the H-D racing team dominated the circuit and were dubbed the "Wrecking Crew." The F-Head was eventually fitted with a short-lived two-speed transmission, followed by a more successful three-speed design. The popularity of Harley Davidson's grew both worldwide and with the U.S. military. So popular, in fact, that Harley Davidson became the world leader in motorcycle production in 1920.

In 1929, a new engine debuted on the D-Models. Affectionately known as the Flathead, this 45 cubic inch engine becomes the class of motorcycle racing power. So dominant is Harley Davidson that only Indian Motorcycles are left as competitors in American motorcycle manufacutring. Known for its reliablility, this engine enjoyed nearly 45 years of service with versions available on models up to 1973.

Knuckleheads, known by their beautifully distinctive rocker boxes, were introduced in 1936. Knuckleheads were Harley Davidson's first Overhead Valve (OHV) design, replacing the side-valve engineered Flatheads. In 1937 Joe Petrali, with his 61 CI Knucklehead engine, traveled over 136 mph setting a new land speed record. HD purists have had a unique fascination with these engines, and they have been called the best-looking power-plants to leave the fair city of Milwaukee. New engine manufacturers, as with the following engines, have resurrected knuckleheads combining the beloved appearance with new technologies.

In 1948 Harley Davidson unveiled and engine that showcased improvements to the valve train of the Knuckleheads, such as hydraulic lifters and aluminum heads. Dubbed Panheads due to the large cake-pan like rocker covers. Harley Davidson celebrates it's 50th anniversary while it's sole competition in America, Indian Motorcycles, goes out of business. 1955 marks the debut of the legendary Sportster, with a 55 CI Panhead on board. Later, the Servicar model is the first HD to receive an electric starter. 

Shovelheads were first seen in 1966. Though improvements were made to the Panheads, from 1966-1969, the new Harley Davidson engines actually used Panhead lower units. The distinct rounded covers that sat atop the enclosed heads gave rise to the Shovelhead nickname. 1979 sees the unveiling of the Fat Bob, followed in 1980 by the first offerings of final drive belts, which soon become standard, and HD ends the 12 year relationship with AMF. Shovelheads are still readily available, both as used and newly manufactured enignes.

It took seven years of development before the Blockhead made it's appearance in 1984, and it provided 15 years of durable service. The Evo engine also marked the introduction of a new Softail. In 1986, a Sportster right-hand drive version is added to the collection. Harley Davidson enjoys expansive success on during the reign of the Evo, with new locations in Kasas City, Menomenee Falls, and Manaus, Brazil. Debuting as an 80 CI engine, the Blockhead has seen great popularity with engine builders and aftermarket manufacturers. For those that crave big horsepower, manufacturers are making Evo-style engines in the 120 CI range.

Unveiled in 1999 the Twin Cam (aka TC, Fathead or Twinkie) engines are the newest of the air-cooled power plants offered by Harley Davidson. Though the engine still incorporates overhead valves and pushrods, the distinction comes form the two cams in the crankcase. The Fathead has both balanced (A models) and unbalanced models (B models) and are available in 88 and 96 CI sizes, the latter being seen in 2006.